KR20130118255A - Cathode active material and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: A positive active material has the combination of a spinel lithium nickel manganese oxide and a specific oxide, thereby improving lifetime and improving capacity and safety even when a lithium titanium oxide is used as a negative active material. CONSTITUTION: A positive active material includes the combination of a spinel-structured lithium nickel manganese composite oxide represented by chemical formula 1: Li_xM_yMn_(2-y)O_(4-z)A_z and an oxide chemical formula 2: y'Li_2M'O_3'-LiM''O_(2-z')A'_z' and has a plateau at 3.0-4.8 V during a first charging. In the chemical formulas, 0.9<=x<=1.2, 0<y<2, and 0<=z<0.2; M is at least one selected from Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi; and A is one or more anions with a valence of -1 or -2.

Description

Cathode Active Material and Lithium Secondary Battery Comprising The Same

The present invention relates to a positive electrode active material and a lithium secondary battery including the same, and to a positive electrode active material having a flat section at 3.0 to 4.8 V during the first charge, including a combination of two specific compounds.

The increase in the price of energy sources due to the depletion of fossil fuels, the increase of interest in environmental pollution, and the demand for environmentally friendly alternative energy sources are becoming indispensable factors for future life. Various researches on power generation technologies such as nuclear power, solar power, wind power, and tidal power have been continuing, and electric power storage devices for more efficient use of such generated energy have also been attracting much attention.

Particularly, in the case of a lithium secondary battery, the demand for an energy source is rapidly increasing due to an increase in technology development and demand for a mobile device. Recently, the use of a lithium secondary battery as a power source for an electric vehicle (EV) and a hybrid electric vehicle , And the area of use is also expanding for applications such as power assisted power supply through gridization.

Conventional lithium ion secondary batteries generally use a lithium metal composite oxide for the positive electrode and a graphite-based material for the negative electrode. However, in recent years, the Li-ion secondary battery has used Li (silicon) using silicon (Si) and tin (Sn). A lot of research on the anode material and lithium titanium oxide by the alloy reaction (alloy).

Lithium titanium oxide has very low structural changes during charging and discharging, and has a zero-strain material, which has excellent life characteristics, forms a relatively high voltage range, and does not generate dendrite, resulting in safety. And materials are known to be very good.

However, even though the theoretical capacity of the lithium titanium oxide is 175 mAh / g, and the capacity is improved to the current level of 160 to 170 mAh / g, there is a problem that the capacity of the conventional carbon-based negative electrode material is insufficient.

Therefore, while using lithium titanium oxide as the negative electrode active material, there is a high need for a technology that can improve the performance of the secondary battery by providing a desired level of capacity characteristics and safety.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application have confirmed that a high-capacity battery can be realized when a lithium spinel manganese composite oxide having a specific spinel structure and a predetermined oxide are used as a positive electrode active material. The present invention has been completed.

Accordingly, the present invention includes a combination of a lithium nickel manganese composite oxide having a spinel structure represented by the following Chemical Formula 1 and an oxide represented by the following Chemical Formula 2, and has a flat section at 3.0 to 4.8 V at the first charge. It provides an active material.

Li _x M _y Mn _{2 - y} O _{4 - z z} (1)

y'Li₂M’O₃? (1-y ’) LiM’’O_{2-z '}A '_{z '}         (2)

In the above formula, 0.9 ≦ x ≦ 1.2, 0 <y <2, 0 ≦ z <0.2, and M is Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, At least one element selected from the group consisting of Nb, Mo, Sr, Sb, W, Ti and Bi, and A is -1 or -divalent one or more anions;

0 <y '<1, 0≤z' <0.2 and M 'is one or more elements selected from Mn, Sn, Zr, etc. having +4, and M' 'has a six coordination structure such as Ni, Mn, Co, etc. At least one element selected from monocycle and bicycle transition metals that are stabilized in the structure, and A 'is at least one anion of -1 or -divalent.

The cathode active material according to the present invention may include a combination of a lithium nickel manganese composite oxide having a predetermined spinel structure and a specific oxide to maintain a high voltage during a charge / discharge process of a battery, and thus may exhibit excellent life characteristics.

In the present invention, the oxide of Formula 1 may be represented by the following formula (3).

Li _x Ni _y Mn _2-y O ₄ (3)

In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5.

In detail, the oxide of Formula 3 may be LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ .

In addition, the oxide of Formula 2 may be represented by the following formula (4).

z'Li ₂ MnO ₃ ? (1-z ') LiM''O ₂ (4)

Where

0.5 <z '<1, M' 'is six or more coordination structures such as Ni, Mn, Co, and is at least one element selected from one-cycle and two-cycle transition metals stabilized in a layered structure.

The average particle diameter (D50) of the secondary particles of the oxide of Formula 1 may be 2 to 30 ㎛, in detail may be 4 to 20 ㎛.

The average particle diameter of the oxide in the present invention means, in detail, the particle size when a plurality of particles (primary particles) aggregate to form one combination (secondary particles). In the positive electrode active material, each oxide unit tends to aggregate with each other to form a combination according to the setting conditions of the manufacturing process, and such agglomerated combination exhibits active material properties by itself. Therefore, the average particle diameter of the oxide specifically means the particle diameter of such an aggregated combination.

The oxide of Formula 2 may be a composite of a layer structure or may be in the form of a solid solution.

In the present invention, the mixing ratio of the two composite oxides may be 50:50 to 99: 1 based on weight, specifically, 80:20 to 95: 5, and more specifically 80:20 to 90: May be ten. The mixing ratio is an optimal range for exerting the desired level of effect, and in particular, if the content of the composite oxide of Formula 2 is too small, it is not preferable because the desired capacity and safety cannot be obtained.

The present invention also provides a secondary battery comprising the cathode active material.

The secondary battery may include a lithium metal oxide represented by Formula 5 as a negative electrode active material.

Li _a M ' _b O _4-c A _c (5)

In the above formula, M 'is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr; a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4; c is determined according to the oxidation number in the range of 0? c <0.2; A is one or more of an anion of -1 or -2.

The lithium metal oxide may be represented by the following formula (6).

Li _a Ti _b O ₄ (6)

In the above formula, 0.5? A? 3, 1? B? 2.5.

The lithium metal oxide may be Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ .

The lithium titanium oxide has a higher potential for lithium than graphite and excellent in safety because lithium reactants and lithium do not precipitate at the interface. However, since lithium titanium oxide has a high potential of about 1.5 V with respect to lithium, when used with a conventionally used positive electrode active material such as lithium cobalt oxide, the discharge voltage of the battery cell drops to about 2.4 V, and the theoretical capacity is also 175 mAh /. It is similar to graphite in g, so there is a limit in improving energy density.

Therefore, in the present invention, using the positive electrode active material defined above, while using lithium titanium oxide as the negative electrode active material can not only maintain a high voltage, but also exhibit excellent capacity and output characteristics.

Methods for preparing the oxides defined above are known in the art, and a description thereof is omitted herein.

The secondary battery according to the present invention includes a cathode prepared by applying a mixture of a cathode active material, a conductive material, and a binder on a cathode current collector, followed by drying and pressing, and a cathode manufactured using the same method, in which case, In some cases, a filler may be further added to the mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel A surface treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 &lt; x &lt; Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide and the like may be used, but in detail, lithium titanium oxide and the like defined above may be used.

The secondary battery may have a structure in which a lithium salt-containing electrolyte is impregnated in an electrode assembly having a separator interposed between a positive electrode and a negative electrode.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The electrolyte solution containing the lithium salt is composed of an electrolyte solution and a lithium salt. The electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte, but is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In one example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) _2, and the like, are linear with cyclic carbonates of EC or PC, which are highly dielectric solvents, and DEC, DMC, or EMC, which are low viscosity solvents. The lithium salt-containing non-aqueous electrolyte can be prepared by adding to a mixed solvent of carbonate.

The present invention also provides a battery module including the secondary battery as a unit cell, and a battery pack including the battery module.

The battery pack can be used as a power source for a medium and large-sized device requiring high temperature stability, long cycle characteristics, and high rate characteristics.

Examples of the medium-large device include a power tool that is driven by an electric motor; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

As described above, the positive electrode active material according to the present invention contains a combination of a lithium nickel manganese composite oxide having a predetermined spinel structure and a specific oxide, thereby exhibiting excellent life characteristics, and remarkably using lithium titanium oxide as a negative electrode active material. Exhibits improved capacity and safety.

1 is a graph measuring the rate of change of voltage and temperature with time of a battery that passed the needle passage test in Experimental Example 2; And
Figure 2 is a graph measuring the rate of change of voltage and temperature with time of the battery that did not pass the needle passage test in Experimental Example 2.

&Lt; Example 1 >

LiNi_0.5Mn_1.5O₄Oxide and 0.6Li₂MnO₃? 0.4LiMnO₂of A positive electrode active material was prepared by mixing oxides in a 90:10 (weight ratio). 90% by weight of this positive electrode active material, 5% by weight of Super-P (conductor) and 5% by weight of PVdF (binder) were added to NMP to prepare a positive electrode mixture. Prepared.

&Lt; Comparative Example 1 &

A positive electrode mixture was prepared in the same manner as in Example 1 except that only LiNi _0.5 Mn _1.5 O _{4 was} used as the positive electrode active material.

<Experimental Example 1>

The positive electrode mixture prepared in Example 1 and Comparative Example 1 was applied to an aluminum current collector to prepare a positive electrode for a secondary battery. 90% by weight of this positive electrode and Li _1.33 Ti _1.67 O ₄ , 5% by weight of Super-C (conductor) and 5% by weight of PVdF (binder) were added to NMP to prepare a negative electrode mixture, which was then applied to an aluminum current collector and dried. And the electrode assembly using a porous separator made of a negative electrode and a polypropylene prepared by pressing. Thereafter, the electrode assembly and then placed in a pouch connected to the lead wire, 1 M of LiPF ₆ salt melt volume ratio of 1 with 1: 1 of ethylene carbonate (EC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC ) Was injected into the electrolyte, and then sealed to assemble a lithium secondary battery in the form of 9 bicells. These batteries are shown in Table 1 below by measuring their capacity under 0.1 C charge and discharge conditions.

Capacity (mAh) Example 1 596 Comparative Example 1 584

According to Table 1, it can be seen that the battery of Example 1 exhibits excellent capacity characteristics compared to the battery of Comparative Example 1.

<Experimental Example 2>

The positive electrode mixture prepared in Example 1 and Comparative Example 1 was applied to an aluminum current collector to prepare a positive electrode for a secondary battery. 90% by weight of this positive electrode and Li _1.33 Ti _1.67 O ₄ , 5% by weight of Super-C (conductor) and 5% by weight of PVdF (binder) were added to NMP to prepare a negative electrode mixture, which was then applied to an aluminum current collector and dried. And the electrode assembly using a porous separator made of a negative electrode and a polypropylene prepared by pressing. Thereafter, the electrode assembly was placed in a pouch, and the lead wires were connected to each other, whereby 1 M of LiPF ₆ salt was dissolved in a volume ratio of 1: 1, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). ) Was injected into the electrolyte, and then sealed to prepare a lithium secondary battery of the form.

The number of batteries passed through the needle penetrator experiment after making 20 secondary batteries each was shown in Table 2 below, and the results of the needle penetrator tests were shown in FIGS. 1 and 2.

Needle penetrating body experiment was performed by penetrating the center of the cell at a rate of 8 cm / s nails with a diameter of 3 mm.

Example 1 Comparative Example 1 Needle penetrator experiment
Passed battery 19 pass 14 pass

As shown in Table 2, the battery according to Example 1 according to the present invention can be confirmed that the number of cells that passed the needle through the experiment compared to the battery according to Comparative Example 1. Therefore, compared with the comparative example 1, safety can be ensured.

According to FIG. 1, in the case of a battery that passed the needle penetrating body test, the temperature and voltage change rate were slow with time. However, according to FIG. 2, in the case of a battery that did not pass the needle penetrating body test, the temperature rapidly increased over time. It can be seen that there is a section in which increases and the voltage drops.

Therefore, it can be seen that the battery according to Example 1 is superior in safety and performance as compared to the battery according to Comparative Example 1.

Those skilled in the art to which the present invention pertains will be able to exercise various applications and modifications within the scope of the present invention based on the above contents.

Claims (18)

A cathode active material comprising a combination of a lithium nickel manganese composite oxide having a spinel structure represented by Formula 1 and an oxide represented by Formula 2 below, and having a flat section at 3.0 to 4.8 V at first charge:
Li_xM_yMn_2-yO_4-zA_z                                (One)
y'Li₂M’O₃? (1-y ’) LiM’’O_{2-z '}A '_{z '}         (2)
In the above formula, 0.9 ≦ x ≦ 1.2, 0 <y <2, 0 ≦ z <0.2, and M is Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, At least one element selected from the group consisting of Nb, Mo, Sr, Sb, W, Ti and Bi, and A is -1 or -divalent one or more anions;
0 <y '<1, 0≤z' <0.2 and M 'is one or more elements selected from Mn, Sn, Zr, etc. having +4, and M' 'has a six coordination structure such as Ni, Mn, Co, etc. At least one element selected from monocycle and bicycle transition metals that are stabilized in the structure, and A 'is at least one anion of -1 or -divalent. The cathode active material of claim 1, wherein the oxide of Formula 1 is represented by the following Formula 3:
Li _x Ni _y Mn _2-y O ₄ (3)
In the above formula, 0.9? X? 1.2 and 0.4? Y? 0.5. The cathode active material of claim 2, wherein the oxide of Formula 3 is LiNi _0.5 Mn _1.5 O ₄ or LiNi _0.4 Mn _1.6 O ₄ . The cathode active material according to claim 1, wherein the oxide of Formula 2 is represented by the following Formula 4.
z'Li ₂ MnO ₃ ? (1-z ') LiM''O ₂ (4)
In this formula,
0.5 <z '<1, M''is one or more elements selected from one-cycle and two-cycle transition metals having a six coordination structure such as Ni, Mn, Co and stabilized in the layered structure. The cathode active material according to claim 1, wherein the average particle diameter (D50) of the secondary particles of the oxide of Formula 1 is 2 to 30 µm. The cathode active material of claim 1, wherein the oxide of Formula 2 is in the form of a layered composite or solid solution. The cathode active material of claim 1, wherein the mixing ratio of the oxide of Formula 1 and the oxide of Formula 2 is 50:50 to 99: 1 by weight. The cathode active material according to claim 7, wherein the mixing ratio of the oxide of Formula 1 and the oxide of Formula 2 is 80:20 to 95: 5 based on the weight. The cathode active material of claim 7, wherein the mixing ratio of the oxide of Formula 1 and the oxide of Formula 2 is 80:20 to 90:10 by weight. A secondary battery comprising the cathode active material according to any one of claims 1 to 9. The secondary battery of claim 10, wherein the secondary battery comprises a lithium metal oxide represented by Formula 5 as a negative electrode active material:
Li _a M ' _b O _4-c A _c (5)
Wherein M '' is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr; a and b are 0.1? a? 4; Is determined according to the oxidation number of M 'in the range of 0.2? B? 4; c is determined according to the oxidation number in the range of 0? c <0.2; A is one or more of an anion of -1 or -2. The method of claim 11, wherein the lithium metal oxide is a secondary battery characterized in that represented by the following formula (6):
Li _a Ti _b O ₄ (6)
In the above formula, 0.5? A? 3, 1? B? 2.5. The secondary battery of claim 12, wherein the lithium metal oxide is Li _1.33 Ti _1.67 O ₄ or LiTi ₂ O ₄ . The secondary battery of claim 10, wherein the secondary battery is a lithium secondary battery. A battery module comprising the secondary battery according to claim 10 as a unit cell. A battery pack comprising the battery module according to claim 15. A device comprising a battery pack according to claim 16. 18. The device of claim 17, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for power storage.

Images